Method of and apparatus for detecting presence or absence of photosensitive object at a prescribed position

ABSTRACT

Photosensors having light emitting elements and light receiving elements are provided in a path for carrying a film. The light emitting elements emit periodic pulsed light. When the film is present in the positions of the photosensors, the periodic pulsed light is reflected by the film to enter the light receiving elements, whereby presence of the film is detected. Activation time and activation interval of the light emitting elements for generating the periodic pulsed light are determined so that accumulated exposure value in each portion on the film is less than a critical exposure value of photosensitive material provided in the film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus foroptically detecting presence or absence of a photosensitive object, suchas a photographic process film, at a prescribed position of a pathcarrying the photosensitive object.

2. Description of the Prior Art

In the field of photographic process or the like, it is generallyrequired to automatically convey a photographic film to a settingposition. Therefore, employed is a photosensitive object detectingapparatus for detecting presence or absence of the film at a prescribedposition thereby to detect the position and width of the film. Such aphotosensitive detecting apparatus is constructed in a contact typeapparatus employing a microswitch etc. or in a non-contact typeapparatus employing light or supersonic waves. Within these types ofapparatus, the former tends to spoil the film.

Therefore, generally employed is a photosensitive object detectingapparatus of the non-contact type, which is most importantly representedby an apparatus of an optical type capable of accurate detection. In theapparatus of the optical type, however, detection light must necessarilybe applied to the photosensitive object, whereby a latent image isinevitably sensitized by the detection light. In order to prevent thissensitization, detection light outside a photosensitive wavelength bandof the film may be employed, and hence near infrared rays are mainlyemployed as detection light for a film for general use. However, imageprocess equipment utilizing semiconductor laser etc. employ aninfrared-photosensitive film, such as a process infrared film, which isinevitably sensitized if ordinary near infrared light is utilized.

However, a light emitting element which emits light having anon-photosensitive wavelength with respect to such a film (wavelength ofa far-infrared band for a process infrared film, for example) isgenerally high-priced, so that the cost of photosensitive objectdetecting apparatus employing the same is increased.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus for opticallydetecting a photosensitive object having a photosensitive materialcarried along a prescribed path in a prescribed position along the path,which apparatus comprises: light emitting means provided oppositely tothe prescribed position; power supply means for supplying pulse power tothe light emitting means thereby to activate the light emitting means toemit pulsated light, in which activation time and activation interval ofthe pulse power is determined to satisfy a condition whereby accumulatedexposure value in each portion on the photosensitive object is less thana critical exposure value of the photosensitive material, depending on aphotosensitive character of the photosensitive material, when the pulsedlight is applied to the photosensitive object being moved; and lightreceiving means facing the prescribed position for receiving the pulsedlight thereby to generate a photosensitive object detection signal forindicating whether or not the photosensitive object is present at theprescribed position.

The present invention also provides a method of detecting edges andwidth of the photosensitive object through the aforementioned apparatus.Since the activation time and the activation interval of the pulsedpower for generating the pulsed light are determined on a condition thatthe accumulated exposure value in each portion on the photosensitiveobject is less than a critical exposure value, the photosensitive objectis detected without generation of a latent image.

The term "critical exposure value" in the present invention is employedto indicate the upper limit value of accumulated exposure value thatdoes not substantially sensitize the employed photosensitive object. The"critical exposure value" depends on the type of the photosensitivematerial and the wavelength of the light emitted from the light emittingmeans.

Accordingly, an object of the present invention is to provide alow-priced photosensitive object detecting apparatus which can detectthe presence or absence of a photosensitive object without substantialsensitizing of the photosensitive object and a method of detecting edgesand width of the photosensitive object employing the apparatus.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial overview of an embodiment of the present invention;

FIG. 1B is a block diagram showing the embodiment in more detail;

FIG. 2 is a perspective view of a photosensor;

FIGS. 3A and 3B are a light emission characteristic diagram of a lightemitting element and a photosensitive spectrum characteristic diagram ofa film;

FIGS. 4 and 5 are diagrams illustrating formats of signals in thepreferred embodiment;

FIG. 6 is a diagram of a pulsed signal;

FIG. 7 is a diagram for explaining how accumulated value is obtained:

FIGS. 8(a) through 9(d) are timing charts of operation for detecting aforward edge through pulsed emission of light;

FIGS. 10 and 12 are block diagrams of edge detection dedicated circuitsusing pulsed light emission and continuous light emission, respectively;

FIG. 11 is a timing chart forward edge detection using continuous lightemission;

FIG. 13 is a diagram illustrating an encoding rule in an encodingcircuit 27; and

FIG. 14 is a diagram showing width detecting operation according to thepreferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a partial arrangement diagram of a preferred embodiment of thepresent invention. FIG. 1B is a block diagram showing the preferredembodiment in detail. This embodiment is structured as an apparatus forperforming edge detection and width detection of a photosensitiveprocess film 1 having photosensitive material, which apparatus isassembled in a process camera (not shown). The film 1 is initiallylocated in an upper position of FIG. 1A, to be downwardly carried forexposure. Rollers 2 are provided in the path for feeding the film 1,which rollers 2 are rotated by a motor M to feed the film 1.

Five photosensors 3 (3a to 3c), 4 and 5 are provided at prescribedpositions along the path. Each of the photosensors 3 to 5 has a lightemitting element 6 and a light receiving element 7 as shown in FIG. 2,to be substantially similar in structure to a so-called reflection typephotoelectric switch. When the film 1 is in a position opposite thelight emitting element 6, light emitted from the light emitting element6 is reflected by the film 1 to enter the light receiving element 7.When there is no film 1, light from the light emitting element 6 doesnot reach the light receiving element 7. Namely, the light receivingelement 7 optically detects whether or not the film 1 is present in anemission path of the light from the light emitting element 6. In thisembodiment, the light emitting element 6 is prepared by a light emittingdiode which emits a light having wavelength band J, shown in FIG. 3A.The film 1 has a photosensitive material whose photosensitive spectrum"photosensitive character" is shown in FIG. 3B, for example. Thewavelength band J of the light emitted from the light emitting element 6partially overlaps with photosensitive wavelength areas K of the film 1.

Within the photosensors 3 to 5, photosensors 4 and 5 are provided forforward edge direction and discharge detection (terminating enddetection) of the film 1, and arranged to face the center line Y (FIG.1A), which is a reference line of the film carrying path. The remainingphotosensors 3a to 3c are adapted to detect the width of the film 1. Thephotosensor 3a is arranged to face the carrier center line Y, while theother two photosensors 3b and 3c are arranged in positions displaced byprescribed distances l₁ and l₂ from the carrier center line Y,respectively. The photosensors 3a to 3c, 4 and 5 are hereinafterreferred to as "width detecting sensors", "forward edge detectingsensor" and "discharge detecting sensor", respectively.

Referring to FIG. 1B, the photosensitive object detecting apparatus hasa detection control circuit 10 which performs light emission control andlight receiving signal processing suitable for purposes of theaforementioned photosensors 3 to 5. This detection control circuit 10 isprovided with a light emission control circuit 12 for performing lightemission control of the light emitting elements 6 in the photosensors 3to 5, and light emission control signals C from the light emissioncontrol circuit 12 are outputted to a selector 21.

The light emission control signals C are four-bit signals for indicatingwhich light emitting element within the photosensors 3 to 5 is activatedto emit light in what mode. As shown in FIG. 4, the light emission modes(pulse light emission, continuous light emission and turn-off) of therespective photosensors 3 to 5 are indicated by logical combination oflevels "H" and "L" of respective bits C₁ to C₄ of the light emissioncontrol signals C.

In response to the light emission control signals C, the selector 21supplies one of a continuous ON voltage (0 [V]), a continuous OFFvoltage (V_(CC) [V]) and a periodic pulse voltage PL to respective onesof the light emitting elements 6 in the photosensors 3 to 5 as lightemission signals B (B₃ to B₅). The pulse voltage PL is generated from apulse generator 22, with pulse width (activation time of thephotosensors 3 to 5) and pulse interval (activation interval of thephotosensors 3 to 5) being set in accordance with a rule as hereinafterdescribed.

These photosensors 3 to 5 are biased by electric potential (+V_(CC))from an electric supply (not shown). Therefore, when the continuous ONvoltage (0 [V]) is supplied as the light emission signal B₄, forexample, continuous light emission power is supplied to the photosensor4 since voltage between the electric potential from the supply and zeropotential is applied to the photosensor 4. Further, when the pulsedlight emission voltage PL is supplied to the photosensor 4, periodicpulsed light emission power is supplied to the photosensor 4. Therefore,a DC power supply (not shown) for providing the potential (+V_(CC))forms means for supplying continuous power, while a combination of theaforementioned power supply and the pulse generator 22 form means forsupplying pulsed power.

The photosensors 3 to 5 are provided in their subsequent stages withflip-flop circuits (hereinafter referred to as "F/F circuits") 23a to23c, 24 and 25 for latching light receiving signals A_(3a) to A_(3c), A₄and A₅ generated at the light receiving elements 7 in the photosensors 3to 5 by converting received lights to electric signals, respectively.Further, the F/F circuits 24 and 23a to 23c are provided in theirsubsequent stages with data selector 26 and an encoding circuit 27having functions as hereinafter described, respectively.

Sensor output signals D (photosensitive material detecting signals)having four bits and passing through these circuits are supplied to asensor output reading circuit 13. FIG. 5 shows the contents indicated bylogical levels "H" and "L" of the sensor outputs D (D₃₁, D₃₂, D₄ andD₅).

On the other hand, the sensor output reading circuit 13 performsdetection of the film 1 (FIG. 1A) on the basis of the logical levels ofthe sensor output signals D, to provide a light emission switchingsignal W and a motor control signal R to the light emission controlcircuit 12 and a motor control circuit 14, respectively, in response tothe result of the detection. An initializing circuit 11 suppliesinitializing signals I₁₂ and I₁₄ to the light emission control circuit12 and the motor control circuit 14, respectively.

B. Pulse Voltage PL

Description is now made of the rule to establish the desired periodicpulse voltage PL waveform. The pulse voltage PL is formed as a periodicpulse train having activation time T_(D) and activation interval T_(I),as shown in FIG. 6. The pulse voltage PL is employed to cause one of thelight emitting elements 6 in the photosensors 3 to 5 to perform pulselight emission. Therefore, the activation time T_(D) and the activationinterval T_(I) are so set that accumulated exposure value of eachportion (each photosensitive position) of the film 1 under the carriageby light from the light emitting element 6 is less than a criticalexposure value which is known from the photosensitive characteristic ofthe film 1. The term "critical exposure value" means the upper limitvalue of accumulated exposure, by which a photosensitive object (film 1)is not substantially sensitized. This is achieved by setting theactivation time T_(D) and the activation interval T_(I) in considerationof the following relation, for example. In the following description,only the forward end detecting sensor 4 is considered, for example, butthe following relation is common to the respective photosensors 3 to 5.

Consider a film 1 which is being downwardly carried at a velocity V, asshown in FIG. 7, and assume that the symbol I represents the amount oflight energy per second of detection light L₁ which is applied on aphotosensitive surface 41 of the film 1. Assume further that the symbold represents the width (diameter) of the detection light L in thecarrying direction and that the symbol X₀ represents a critical exposurevalue of the film 1. Then, the photosensitive position P in FIG. 7 issubjected to the exposure of:

    X.sub.1 =IT.sub.D                                          (1)

per one pulse emission. The time T required for passage of thephotosensitive position P through a section of the width d by thecarriage of the film 1 is:

    T=d/V                                                      (2)

Then, the photosensitive position P is subjected to pulsed lightemission of:

    N=T/(T.sub.D +T.sub.1)                                     (3)

times during the time T.

As a result, the accumulated exposure value X in the photosensitiveposition P is:

    X=X.sub.1 N=(I T.sub.D T)/(T.sub.D +T.sub.I)               (4)

From the condition that the accumulated exposure value X in eachphotosensitive position is less than the critical exposure value X₀, thefollowing expression (5) or an expression (6) equivalent thereto can beobtained:

    (I T.sub.D T)/(T.sub.D +T.sub.I)≦X.sub.0            (5)

    [(I.sub.d /V)-X.sub.0 ]T.sub.d ≦X.sub.0 T.sub.I     (6)

The critical exposure value X₀ has a value depending on thephotosensitive character of the photosensitive material of the film 1,which is determined both from the type of photosensitive materialprovided in the film 1 and the wavelength of the light. When the time Trequired for passage of the photosensitive position P through thesection of the width d is shorter than the light emission period, i.e.,activation period (T_(D) +T_(I)), an expression N≦1 is obtained andhence a relation X≦X₁ is found the expression (4). In this case,therefore, the activation time T_(D) may be decided to satisfy:

    TD≦X.sub.0 /I                                       (7)

from the condition of X₁ ≦X₀.

In this example, it is assumed that d ≈6 mm, V=8.4mm/sec. and (T_(D)+T_(I))=1 sec. Therefore,

    T=6/8.4=0.71 [sec.]<1[sec.]                                (8)

holds and the activation time T_(D) may be set by the expression (7).

Therefore, when (X₀ /I)=0.2, for example, it may be calculated thatT_(D) ≦0.2 [sec.] from the expression (7), and preferably the activationtime T_(D) is determined to be less by several multiples of tens thanthe value obtained by (X₀ /I). In this embodiment, it is calculated thatT_(D) =1 [msec.] with respect to the case of (X₀ /I)=0.2 to 0.3.

C. Forward Edge Detecting Operation (Pulse Light Emission)

Under the aforementioned conditions, description is now made on aprocedure detecting the film forward edge 42 of FIG. 1A using periodicpulse light emission. In operation, the initializing circuit 11 of FIG.1B first generates the initializing signals I₁₂ and I₁₄. Thus, the motorM is rotated to start movement of the film 1, while light emissioncontrol circuit 12 outputs a light emission control signal:

    C="C.sub.4 C.sub.3 C.sub.2 C.sub.1 "="HHLL"

According to the rule of FIG. 4, this means that the light emittingelement 6 in the forward edge detecting sensor 4 is adapted to receivepulsed light emission and the light emitting elements 6 in the otherphotosensors 3 and 5 are turned off. Therefore, the elector 21 operatesto supply the pulse voltage PL to the forward edge detecting sensor 4,while the continuous OFF voltage is supplied to the width detectingsensors 3 and the discharge detecting sensor 5. Thus, only the lightemitting element 6 in the forward edge detecting sensor 4 periodicallyperforms pulsed light emission in accordance with the pulse train ofFIG. 6, while the other photosensors 3 and 5 remain turned off.

On the other hand, the light receiving signal A₄ from the forward edgedetecting sensor 4 becomes a latch output AL₄ through the F/F circuit24, to be supplied to the data selector 26. Latch timing in the F/Fcircuit 24 is determined by timing of the pulse voltage PL. The lightreceiving signal A₄ is directly supplied as other data input of the dataselector 26.

Second lower order data bit C₂ within the light emission control signalsC is supplied as a selection signal for the data selector 26. The latchoutput AL₄ is selected in the case of the pulse emission as hereinconsidered, i.e., when C₂ ="L", to be outputted to the sensor outputreading circuit 13 as a sensor output signal D₄. Determination in thesensor output reading circuit 13 as to which sensor detects light isperformed by the rule of FIG. 5.

Consider such a case wherein the film 1 of FIG. 1A is graduallydownwardly carried so that its forward edge 42 reaches the position ofthe forward edge detecting sensor 4 at a time t₁. Then, the film 1 is"present" in the position of the forward edge detecting sensor 4 aftert= t₁, as shown in FIG. 8(a). The light receiving signal A₄ is activated(G₁ in FIG. 8(c)) in first pulse light emission (F₁ in FIG. 8(b)) aftert=t₁, to be latched in the F/F circuit 24 (H₁ in FIG. 8(d)). The latchoutput AL₄ is applied as the sensor output signal D₄. Thus, the sensoroutput reading circuit 13 performs forward edge detection at a time t₂in FIG. 8(d).

When a rear edge 43 (refer to FIG. 1A) of the film 1 passes through theposition of the forward edge detecting sensor 4 at t=t₃ of FIG. 8(a),the latch output AL₄ (FIG. 8(d)) falls in response to first pulseemission F₂. Thus, the respective circuits return to initial states.Since pulse light emission is appropriately performed in this operationby setting its width and interval using the rule (5), (6) or (7), thefilm 1 is not substantially sensitized.

While the above description has been made for the case of performingonly forward edge detection, the following description is made for thecase of turning off light emission upon forward edge detection. FIG. 9is a timing chart of this case, while operation to forward edgedetection at t=t₂ is similar to that in FIG. 8. In this case, however,the sensor output reading circuit 13 applies a light emission switchingsignal W upon forward edge detection at t=t₂ to the light emissioncontrol circuit 12. Thus, the light emission control circuit 12 switchesthe light emission control signal C to "HH*H", where the symbol "*"indicates either "H" or "L". As a result, the forward edge detectingsensor 4 is supplied with a continuous OFF voltage in accordance withFIG. 4, to be disabled. Thus, the light emitting element 6 in theforward edge detecting sensor 4 is turned off, and thereafter lightemitting receiving operation of the forward edge detecting sensor 4 isterminated (FIG. 9(a) and 9(b)).

When the pulse generator 22 generates a subsequent pulse (not shown),the light receiving signal A₄ (="L") is latched, and the latch outputsignal AL₄ returns at t=t₄ as shown in FIG. 9(d). Thus, forward edgedetection and turn off of emission by the same are completed. Althoughonly emission turn off is performed in this case, movement of the film 1may be stopped at the same time.

An apparatus as shown in FIG. 10 may be employed as a dedicatedapparatus for performing only the aforementioned forward edge detectionby pulse light emission. In this case, the light emission signal B₄ isdirectly outputted from the light emission control circuit 12.

D. Foward Edge Detecting Operation (Continuous Emission)

In the apparatus shown in FIGS. 1A and 1B, detecting operation such asfoward edge detection can be also performed by continuous lightemission, in addition to detection by pulse light emission. Descriptionis now made of forward edge detecting operation by continuous emission.

In this case, the light emission control circuit 12 of FIG. 1A outputs:

    C="HHHL"

as the light emission signal C, in response to an external selectioninput signal (not shown). Then, the selector 21 performs a selectingoperation using the relation of FIG. 4, to supply a continuous ONvoltage for continuous light emission to the forward edge detectingsensor 4. As a result, the forward edge detecting sensor 4 continuouslyemits light. The data selector 26, being supplied with the signal C₂="H", selects the light receiving signal A₄ from the forward edgedetecting sensor 4 to output the same.

Therefore, when the forward edge 42 of the film 1 reaches the positionof the forward edge detecting sensor 4 at a time t=t₁₀ , the level ofthe light receiving signal A₄ goes high (FIG. 1B). The light receivingsignal A₄ is supplied directly to the sensor output reading circuit 13as the sensor output signal D₄. Then, the sensor output reading circuit13 outputs the light emission switching signal W similarly to theaforementioned case of pulse light emission, whereby the light emissioncontrol signal C becomes:

    C="HH*H" (all off)

Thus, light emission of the forward edge detecting sensor 4 is turnedoff (FIG. 11(c)). The motor control signal R also indicates a stop (FIG.11(d), and the motor M stops in response thereto.

Forward edge detection by continuous light emission and stoppage ofemission/carriage are thus executed. Since the detection by continuouslight emission is combined with the aforementioned stopping operation,the light emission is also stopped immediately after detection light isfirst applied to the film 1. As a result, the film 1 can be preventedfrom being sensitized. FIG. 12 shows a dedicated circuit substantiallyrelating to the continuous light emission mode obtained by extractingonly a portion from the apparatus of FIG. 1B.

E. Terminating Edge Detection (Discharge Detection)

Operation for detecting a terminating edge 43 (refer to FIG. 1A) of thefilm 1 through the apparatus of FIG. 1B is substantially similar to thatin the case of the aforementioned forward edge detection (periodic pulselight emission) except that the discharge detecting sensor 5 is employedto carry out terminating edge detection in response to falling of thesensor output signal D₅. Namely, assuming that the light emissioncontrol signal C is:

    C="LH*H",

only the discharge detecting sensor 5 performs pulse light emission. Theoperation in this case is obtained by replacing:

    B.sub.4 → B.sub.5, A.sub.4 →A.sub.5

    AL.sub.4 → AL.sub.5, D.sub.4 → D.sub.5

in FIG. 8. Therefore, when the terminating edge 43 passes through theposition of the discharge detecting sensor 5 at t=t₃, terminating edgedetection is performed at t=t₄.

F. Width Detection

In order to perform width detection of the film 1, the light emissioncontrol signal C is set to be:

    C="HL*H"

Then, in accordance with the relation of FIG. 4, the selector 21 outputsthe pulse voltage PL as the light emission signal B₃ for the widthdetecting sensors 3a to 3c.

The light receiving signals A_(3a) to A_(3c) from the width detectingsensors 3a to 3c are latched by the F/F circuits 23a to 23c, to becomelatch outputs AL_(3a) to AL_(3c). The three-bit signals are converted bythe encoding circuit 27 to two-bit sensor output signals D₃, and FIG. 13shows the encoding rule thereof.

Therefore, when it is assumed that three types of films 6 inches (15.24cm), 8 inches (20.32 cm) or 10 inches (25.4 cm) in width is providedwith displacement values l₁ and l₂ in FIG. 1A of l₁ =3.5 inches (8.75cm) and l₂ =4.5 inches (11.43 cm), combinations of levels of sensoroutput signals D₃₁ and D₃₂, as shown in FIGS. 14A to 14C, are obtainedfor the respective films. Referring to FIG. 14, t=t₂₀ indicates a timeat which the forward edge 42 of the film 1 reaches the location of thewidth detecting sensors 3. When the sensor output signals D₃₁ and D₃₂are decoded in the sensor output reading circuit 13, in accordance withthe rule of FIG. 5, the width of the film 1 can be detected. Lightemission of the light emitting elements 6 in the photosensors 3 orrotation of the motor M can be stopped as needed, similarly to the caseof forward edge detection.

Also in the case of width detection, the activation time T_(D) andactivation interval T_(I) for the light emitting elements 6 in the threewidth detecting sensors 3a to 3c are set in accordance with theexpression (5) or (7), whereby the film 1 is not substantiallysensitized.

G. Results of Actual Measurement

Experiments have been made to confirm the degree of sensitization in thecase of such photosensitive material detection.

(a) Conditions

(1) Film 1 . . . Near infrared process film having the photosensitivecharacteristic of FIG. 3B and standard photosensitivity of 5 μJ/cm² withrespect to 0.1 μsec. Employed were halftone films subjected to exposureat halftone dot area rates of 50% and 16%, in order to observe influenceto exposed films. The diameter of a single light spot for exposureemployed for forming the halftone dots was about 21 μm (exposurewavelength: 780 to 800 nm). At this time, exposure was performed for10⁻⁷ sec. with each exposure beam, and exposure beam intensity was about220 μW/sec.

(2) Photosensor (light emitting element 6) . . . The photosensoremployed is one comprising a light emitting element having a wavelengthband corresponding to FIG. 3A with a peak at 940 nm, whose measuredvalue of light emission intensity in 950 nm wavelength is about 34W/sec.

(3) Distance between Photosensor and Film Surface . . . 5 mm

(4) Pulse Voltage Waveform . . . Pulses having an activation period(T_(D) +T_(I)) of 1 sec. and an activation time T_(D) of 1 msec. Actualmeasurement was also performed with a one-shot pulse having anotheractivation time as T_(D), for the purpose of comparison.

(b) Results

(1) In the case of 50% halftone dot, T_(D) =0.2 to 0.3 sec. is requiredto perform such photosensitization that the halftone dot is increased insize by emission of the light emitting element. On the other hand, therewas no substantial influence with T_(D) =1 msec., as in the preferredembodiment. The latter is about 1/200 to 1/300 of the former, and theproblem of sensitization is for practical purposes prevented.

(2) In the case of 16% halftone dots, no influence was observed with 1msec., and no sensitization was practically performed with T_(D) =10msec. and 100 msec. This applied to both microscopic observation anddensitometer measurement. The base of the halfdot was blackened to someextent with T_(D) =1 sec., and the optical density value was increasedby about (+0.02).

With these results, it has been experimentally ascertained that theexposure value of a film by light emission of the photosensor of thepreferred embodiment is less than critical exposure value when T_(D) isabout 1 msec., and photosensitization by the same is negligible.

H. Modifications

Although forward edge detection and width detection are independentlyperformed in the aforementioned embodiment, the same may besimultaneously performed. Various control and detection may be performedthrough a microcomputer. The activation time and the activation intervalfor the light emitting elements in pulse light emission are preferablyas small as possible so far as the conditions of the present inventionare satisfied and effective light receiving signals are obtained, sincedetection errors in forward edge detection and the like are reduced asthe values of the activation time and interval are decreased.

Although pulse light emission and continuous light emission can bearbitrarily selected in the example shown in FIG. 1B, an apparatushaving only one function within the same is also employable. When theseare combined, generality of the apparatus is further improved sincehighly accurate detection in continuous light emission and lowphotosensitivity in pulse light emission can be freely selected in asingle apparatus. In order to stop carriage of a film, first and secondphotosensors can be provided for forward edge detection to roughlydetect presence or absence by pulse light emission of a light emittingelement in the first photosensor and thereafter perform continuous lightemission of the second photosensor, thereby to perform fine adjustmentof the position of stoppage of the film.

Confirmation as to whether or not accumulated exposure value by pulselight emission with a trial waveform is less than critical exposurevalue may be either theroretically or experimentally performed, and anactual waveform is determined on the basis of a confirmation.

In the case of carrying a photosensitive object while always aligning aside edge with a specific line but not about the carriage center line Yas in the aforementioned embodiment, the specific line is employed as a"carriage reference line".

When only two types of films, 6 inches and 8 inches, are employed, thephotosensor 3c may be omitted. In the case of two types of films, 8inches and 10 inches, the photosensor 3a or 3b may be omitted. Namely,one or a plurality of photosensors may be provided in response to thenumber of widths of the employed photosensitive objects.

In the example as shown in FIG. 1A, the photosensors 3a, 4 and 5 areprovided facing the carrier reference line and a portion of thephotosensitive surface of the film 1 located on the carrier referenceline receives the light from the photosensors 3a, 4 and 5 duringcarriage on the path. In this case, therefore, pulsed light which makesthe sum of respective accumulated exposure values from the photosensors3a, 4 and 5 less than the critical exposure, is employed. It has beenexperimentally confirmed that the aforementioned example (T_(D) +T_(I)=1 sec, T_(D) =1 msec.) satisfies this condition too. However, such acondition may not be considered if the positional relation between thephotosensors 3a, 4 and 5 and the carrier reference line is displacedslightly.

The light emitting elements 6 and the light receiving elements 7 may beoppositely provided so that a film passes between these elements andlight enters the light receiving elements 7 when a film 43 is presentbetween these elements. In this case, the light receiving element 7faces the light emitting element 6 across the center line Y.

In addition to the photographic film, the present invention isapplicable to other photosensitive objects such as a photographic dryplate. Further, the present invention is applicable to an automaticdeveloping machine etc., in addition to a process camera.

According to the present invention, as hereinabove described, lightemitting means are made to perform pulsed light emission for detecting aphotosensitive object, while activation time and activation interval ofthe emitted light pulses are appropriately selected using a prescribedrule, whereby a photosensitive object detecting method capable ofdetecting presence or absence of the photosensitive object withoutsubstantial sensitizing of the photosensitive object can be obtained.Further, light emitting elements generating light within anon-photosensitive wavelength may not be used but white light emittingmeans, for example, may be employed for detecting various photosensitivematerials, whereby a photosensitive object detecting apparatus can beformed at a low cost.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. An apparatus for optically detecting aphotosensitive object having photosensitive material carried along aprescribed path at a prescribed position along said path, said apparatuscomprising:light emitting means facing said prescribed position; firstpower supply means for supplying pulsed power to said light emittingmeans thereby to activate said light emitting means to emit pulsedlight, an activation time and an activation interval of said pulsedpower being determined to satisfy such a condition that an accumulatedexposure value in each portion on said photosensitive object is lessthan a critical exposure value of said photosensitive material dependingon a photosensitive character of said photosensitive material when saidpulsed light is applied to said photosensitive object being moved:second power supply means for supplying continuous power to said lightemitting means thereby to activate said light emitting means to emitcontinuous light; selection means for selectively enabling one of saidfirst and second power supply means in response to an externallysupplied selection signal thereby to activate said light emitting meansselectively to emit one of said pulsed light and said continuous light;and light receiving means facing said prescribed position for receivinglight emitted from said light emitting means thereby to generate aphotosensitive object detection signal indicating whether or not saidphotosensitive object is present at said prescribed position.
 2. Anapparatus in accordance with claim 1, further including disabling meansfor disabling said first or second power supply means selected by saidselected means when said photosensitive object detection signalindicates a presence of said photosensitive object.
 3. An apparatus inaccordance with claim 2, whereinsaid apparatus is an edge detectingapparatus for detecting the edge of said photosensitive object, saidapparatus further including stop signal generating means for generatinga stop signal for stopping movement of said photosensitive object whensaid photosensitive object detection signal indicates a presence of saidphotosensitive object.
 4. An apparatus in accordance with claim 2,whereinsaid light emitting means and said light receiving means includea light emitting element and a light receiving element provided atpositions displaced from a center line of said path for carrying saidphotosensitive object, respectively, and said apparatus being adapted todetect a width of said photosensitive object.
 5. A method of opticallydetecting an edge of a photosensitive object having a photosensitivematerial carried along a prescribed path at a prescribed position insaid path using light emitting means and light receiving means atpositions facing said prescribed positions of said path, said methodcomprising the steps of:selectively supplying pulsed and continuouspower to said light emitting means in response to an externally suppliedselection signal thereby to selectively activate said light emittingmeans to emit pulsed and continuous light, respectively, an activationtime and an activation interval of said selectively emitted pulsed andcontinuous power being such that an accumulated exposure value in eachportion on said photosensitive object is less than a critical exposurevalue of said photosensitive material; receiving said pulsed selectivelyemitted pulsed and continuous light by said light receiving means; anddetecting said edge of said photosensitive object reaching a positionacross an emission path of said selectively emitted pulsed andcontinuous light by observing an output of said light receiving means.6. A method in accordance with claim 5, further including a step ofstopping a supply of said pulsed and continuous power to said lightemitting means after a detection of said edge.
 7. A method in accordancewith claim 6, further including a step of stopping movement of saidphotosensitive object after a detection of said edge.
 8. A method ofoptically detecting a width of a photosensitive object having aphotosensitive material carried along a prescribed path at a prescribedposition of said path using light emitting means and light receivingmeans at positions displaced by predetermined distances from a centerline of said path, said method comprising the steps of:selectivelysupplying pulsed and continuous power to said light emitting means inresponse to an externally supplied selection signal to selectivelyactivate said light emitting means to emit pulsed and continuous light,respectively, an activation time and an activation interval of saidpulsed and continuous power being such that an accumulated exposurevalue in each portion on said photosensitive object is less than acritical exposure value of said photosensitive material; receiving saidlight selectively emitted by said light emitting means by said lightreceiving means; and detecting a width of said photosensitive object byobserving an output of said light receiving means.
 9. A method inaccordance with claim 8, further including a step of stopping a supplyof said pulsed and continuous power to said light emitting means after adetection of said width.